The present invention relates generally to electro-optical systems, and more specifically, to a system that provides for line of sight stabilization and auto alignment of off-gimbal passive and active electro-optical sensors.
The assignee of the present invention manufactures electro-optical systems, such as forward looking infrared (IR) receivers and laser designator/range receiver systems, for example, that include passive and active sensors. A typical electro-optical system includes subsystems that are located on a gimbal while other subsystems that are located off of the gimbal.
Some off-gimbal sensor and laser systems have no auto-alignment of the sensor and laser lines of sight nor any compensation for any motion due to vibration, thermal or g-force angular deformation in and between the two optical paths. Large errors between the sensor and laser lines of sight are present that limit the effective laser designation ranges, weapon delivery accuracy, and target geo-location capability, all of which require precise laser and sensor(s) line of sight alignment and stabilization.
The resolution and stabilization requirements for third generation tactical airborne infrared (IR) systems are in the same order of magnitude as those required by space and strategic systems, but with platform dynamics and aerodynamic disturbances that are orders of magnitude higher, even above those encountered by tactical surface systems. The environments of third generation airborne system approach both extremes and can change rapidly during a single mission. However, conformance to the physical dimensions of existing fielded system is a driving constraint in their design.
Ideally, a high resolution imaging and laser designation system in a highly dynamic disturbance environment would typically have, at least, a four gimbal set, with two outer coarse gimbals attenuating most of the platform and aerodynamic loads and the two inner most, flexure suspended gimbals providing fine stabilization, with the inertial measurement unit (IMU), IR and visible imaging sensors, and a designating/ranging laser located on the inner most inertially stabilized gimbal.
To reduce gimbal size, weight and cost, the assignee of the present invention has developed a pseudo inner gimbal set for use on various tactical airborne and airborne surveillance systems. This pseudo inner gimbal set uses miniature two-axis flexure suspended mirrors mounted on the inner gimbal together with the IMU and IR sensor, in a residual inertial position error feedforward scheme. The pseudo inner gimbal set replaces the two innermost fine gimbals, while maintaining equivalent performance. With increasing aperture size and constraints required to maintain the size of existing fielded systems, some tactical airborne IR systems are forced to locate the IR and visible sensors and laser off the gimbals using an optical relay path.
In order to re-establish the ideal configuration, an on-gimbal IR sensor(s) and laser configuration can be implemented with an active auto-alignment scheme employing miniature two-axis mirrors, laser reference source(s) and a photodetector. An active auto-alignment and fine stabilization configuration would in effect be equivalent to having the IR sensor(s) and auxiliary components, such as a laser, all mounted on the stabilized inner gimbal. This configuration may be used with any off gimbal multi-sensor system requiring a coincident and stabilized line of sight (LOS), such as targeting systems, and the like.
A previously developed off-gimbal sensor and laser auto-alignment system developed by the assignee of the present invention that provides for such an auto-alignment scheme is disclosed in U.S. Pat. application Ser. No. 09/152,952, filed Sep. 14, 1998, entitled "System for Pseudo On-Gimbal, Automatic Line-of-sight Alignment and Stabilization of Off-Gimbal Electro-Optical Passive and Active Sensors". This system has a separate two-axis mirror on an inner gimbal to perform the enhanced line of sight stabilization function to dynamically steer both beams along laser and IR sensor lines of sight. The steering command to the stabilization mirror is the residual position error of inertial rate loops that inertially stabilize the inner gimbal. An on-gimbal auto-alignment photodetector is operated at null.
It is an objective of the present invention to provide for an improved system that provides for line of sight stabilization and auto alignment of off-gimbal passive and active electro-optical sensors, and which improves upon the system disclosed in the above-identified patent application.